<?php
/**
 * Copyright 2011 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License. You may obtain
 * a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

if (!function_exists('curl_init'))
{
	throw new Exception('Facebook needs the CURL PHP extension.');
}
if (!function_exists('json_decode'))
{
	throw new Exception('Facebook needs the JSON PHP extension.');
}

/**
 * Thrown when an API call returns an exception.
 *
 * @author Naitik Shah <naitik@facebook.com>
 */
class FacebookApiException extends Exception
{
	/**
	 * The result from the API server that represents the exception information.
	 */
	protected $result;

	/**
	 * Make a new API Exception with the given result.
	 *
	 * @param array $result The result from the API server
	 */
	public function __construct($result)
	{
		$this -> result = $result;

		$code = isset($result['error_code']) ? $result['error_code'] : 0;

		if (isset($result['error_description']))
		{
			// OAuth 2.0 Draft 10 style
			$msg = $result['error_description'];
		}
		else
		if (isset($result['error']) && is_array($result['error']))
		{
			// OAuth 2.0 Draft 00 style
			$msg = $result['error']['message'];
		}
		else
		if (isset($result['error_msg']))
		{
			// Rest server style
			$msg = $result['error_msg'];
		}
		else
		{
			$msg = 'Unknown Error. Check getResult()';
		}

		parent::__construct($msg, $code);
	}

	/**
	 * Return the associated result object returned by the API server.
	 *
	 * @return array The result from the API server
	 */
	public function getResult()
	{
		return $this -> result;
	}

	/**
	 * Returns the associated type for the error. This will default to
	 * 'Exception' when a type is not available.
	 *
	 * @return string
	 */
	public function getType()
	{
		if (isset($this -> result['error']))
		{
			$error = $this -> result['error'];
			if (is_string($error))
			{
				// OAuth 2.0 Draft 10 style
				return $error;
			}
			else
			if (is_array($error))
			{
				// OAuth 2.0 Draft 00 style
				if (isset($error['type']))
				{
					return $error['type'];
				}
			}
		}

		return 'Exception';
	}

	/**
	 * To make debugging easier.
	 *
	 * @return string The string representation of the error
	 */
	public function __toString()
	{
		$str = $this -> getType() . ': ';
		if ($this -> code != 0)
		{
			$str .= $this -> code . ': ';
		}
		return $str . $this -> message;
	}

}

/**
 * Provides access to the Facebook Platform.  This class provides
 * a majority of the functionality needed, but the class is abstract
 * because it is designed to be sub-classed.  The subclass must
 * implement the four abstract methods listed at the bottom of
 * the file.
 *
 * @author Naitik Shah <naitik@facebook.com>
 */
abstract class BaseFacebook
{
	/**
	 * Version.
	 */
	const VERSION = '3.2.0';

	/**
	 * Signed Request Algorithm.
	 */
	const SIGNED_REQUEST_ALGORITHM = 'HMAC-SHA256';

	/**
	 * Default options for curl.
	 */
	public static $CURL_OPTS = array(
		CURLOPT_CONNECTTIMEOUT => 10,
		CURLOPT_RETURNTRANSFER => true,
		CURLOPT_TIMEOUT => 60,
		CURLOPT_SSL_VERIFYHOST=>FALSE,
		CURLOPT_SSL_VERIFYPEER=>FALSE,
		CURLOPT_USERAGENT => 'facebook-php-3.2',
	);

	/**
	 * List of query parameters that get automatically dropped when rebuilding
	 * the current URL.
	 */
	protected static $DROP_QUERY_PARAMS = array(
		'code',
		'state',
		'signed_request',
	);

	/**
	 * Maps aliases to Facebook domains.
	 */
	public static $DOMAIN_MAP = array(
		'api' => 'https://api.facebook.com/',
		'api_video' => 'https://api-video.facebook.com/',
		'api_read' => 'https://api-read.facebook.com/',
		'graph' => 'https://graph.facebook.com/',
		'graph_video' => 'https://graph-video.facebook.com/',
		'www' => 'https://www.facebook.com/',
	);

	/**
	 * The Application ID.
	 *
	 * @var string
	 */
	protected $appId;

	/**
	 * The Application App Secret.
	 *
	 * @var string
	 */
	protected $appSecret;

	/**
	 * The ID of the Facebook user, or 0 if the user is logged out.
	 *
	 * @var integer
	 */
	protected $user;

	/**
	 * The data from the signed_request token.
	 */
	protected $signedRequest;

	/**
	 * A CSRF state variable to assist in the defense against CSRF attacks.
	 */
	protected $state;

	/**
	 * The OAuth access token received in exchange for a valid authorization
	 * code.  null means the access token has yet to be determined.
	 *
	 * @var string
	 */
	protected $accessToken = null;

	/**
	 * Indicates if the CURL based @ syntax for file uploads is enabled.
	 *
	 * @var boolean
	 */
	protected $fileUploadSupport = false;

	/**
	 * Indicates if we trust HTTP_X_FORWARDED_* headers.
	 *
	 * @var boolean
	 */
	protected $trustForwarded = false;

	/**
	 * Initialize a Facebook Application.
	 *
	 * The configuration:
	 * - appId: the application ID
	 * - secret: the application secret
	 * - fileUpload: (optional) boolean indicating if file uploads are enabled
	 *
	 * @param array $config The application configuration
	 */
	public function __construct($config)
	{
		$this -> setAppId($config['appId']);
		$this -> setAppSecret($config['secret']);
		if (isset($config['fileUpload']))
		{
			$this -> setFileUploadSupport($config['fileUpload']);
		}
		if (isset($config['trustForwarded']) && $config['trustForwarded'])
		{
			$this -> trustForwarded = true;
		}
		$state = $this -> getPersistentData('state');
		if (!empty($state))
		{
			$this -> state = $state;
		}
	}

	/**
	 * Set the Application ID.
	 *
	 * @param string $appId The Application ID
	 * @return BaseFacebook
	 */
	public function setAppId($appId)
	{
		$this -> appId = $appId;
		return $this;
	}

	/**
	 * Get the Application ID.
	 *
	 * @return string the Application ID
	 */
	public function getAppId()
	{
		return $this -> appId;
	}

	/**
	 * Set the App Secret.
	 *
	 * @param string $apiSecret The App Secret
	 * @return BaseFacebook
	 * @deprecated
	 */
	public function setApiSecret($apiSecret)
	{
		$this -> setAppSecret($apiSecret);
		return $this;
	}

	/**
	 * Set the App Secret.
	 *
	 * @param string $appSecret The App Secret
	 * @return BaseFacebook
	 */
	public function setAppSecret($appSecret)
	{
		$this -> appSecret = $appSecret;
		return $this;
	}

	/**
	 * Get the App Secret.
	 *
	 * @return string the App Secret
	 * @deprecated
	 */
	public function getApiSecret()
	{
		return $this -> getAppSecret();
	}

	/**
	 * Get the App Secret.
	 *
	 * @return string the App Secret
	 */
	public function getAppSecret()
	{
		return $this -> appSecret;
	}

	/**
	 * Set the file upload support status.
	 *
	 * @param boolean $fileUploadSupport The file upload support status.
	 * @return BaseFacebook
	 */
	public function setFileUploadSupport($fileUploadSupport)
	{
		$this -> fileUploadSupport = $fileUploadSupport;
		return $this;
	}

	/**
	 * Get the file upload support status.
	 *
	 * @return boolean true if and only if the server supports file upload.
	 */
	public function getFileUploadSupport()
	{
		return $this -> fileUploadSupport;
	}

	/**
	 * DEPRECATED! Please use getFileUploadSupport instead.
	 *
	 * Get the file upload support status.
	 *
	 * @return boolean true if and only if the server supports file upload.
	 */
	public function useFileUploadSupport()
	{
		return $this -> getFileUploadSupport();
	}

	/**
	 * Sets the access token for api calls.  Use this if you get
	 * your access token by other means and just want the SDK
	 * to use it.
	 *
	 * @param string $access_token an access token.
	 * @return BaseFacebook
	 */
	public function setAccessToken($access_token)
	{
		$this -> accessToken = $access_token;
		return $this;
	}

	/**
	 * Extend an access token, while removing the short-lived token that might
	 * have been generated via client-side flow. Thanks to http://bit.ly/b0Pt0H
	 * for the workaround.
	 */
	public function setExtendedAccessToken()
	{
		try
		{
			// need to circumvent json_decode by calling _oauthRequest
			// directly, since response isn't JSON format.
			$access_token_response = $this -> _oauthRequest($this -> getUrl('graph', '/oauth/access_token'), $params = array(
				'client_id' => $this -> getAppId(),
				'client_secret' => $this -> getAppSecret(),
				'grant_type' => 'fb_exchange_token',
				'fb_exchange_token' => $this -> getAccessToken(),
			));
		}
		catch (FacebookApiException $e)
		{
			// most likely that user very recently revoked authorization.
			// In any event, we don't have an access token, so say so.
			return false;
		}

		if (empty($access_token_response))
		{
			return false;
		}

		$response_params = array();
		parse_str($access_token_response, $response_params);

		if (!isset($response_params['access_token']))
		{
			return false;
		}

		$this -> destroySession();

		$this -> setPersistentData('access_token', $response_params['access_token']);
	}

	/**
	 * Determines the access token that should be used for API calls.
	 * The first time this is called, $this->accessToken is set equal
	 * to either a valid user access token, or it's set to the application
	 * access token if a valid user access token wasn't available.  Subsequent
	 * calls return whatever the first call returned.
	 *
	 * @return string The access token
	 */
	public function getAccessToken()
	{
		if ($this -> accessToken !== null)
		{
			// we've done this already and cached it.  Just return.
			return $this -> accessToken;
		}

		// first establish access token to be the application
		// access token, in case we navigate to the /oauth/access_token
		// endpoint, where SOME access token is required.
		$this -> setAccessToken($this -> getApplicationAccessToken());
		$user_access_token = $this -> getUserAccessToken();
		if ($user_access_token)
		{
			$this -> setAccessToken($user_access_token);
		}

		return $this -> accessToken;
	}

	/**
	 * Determines and returns the user access token, first using
	 * the signed request if present, and then falling back on
	 * the authorization code if present.  The intent is to
	 * return a valid user access token, or false if one is determined
	 * to not be available.
	 *
	 * @return string A valid user access token, or false if one
	 *                could not be determined.
	 */
	public function getUserAccessToken()
	{
		// first, consider a signed request if it's supplied.
		// if there is a signed request, then it alone determines
		// the access token.
		$signed_request = $this -> getSignedRequest();
		if ($signed_request)
		{
			// apps.facebook.com hands the access_token in the signed_request
			if (array_key_exists('oauth_token', $signed_request))
			{
				$access_token = $signed_request['oauth_token'];
				$this -> setPersistentData('access_token', $access_token);
				return $access_token;
			}

			// the JS SDK puts a code in with the redirect_uri of ''
			if (array_key_exists('code', $signed_request))
			{
				$code = $signed_request['code'];
				$access_token = $this -> getAccessTokenFromCode($code, '');
				if ($access_token)
				{
					$this -> setPersistentData('code', $code);
					$this -> setPersistentData('access_token', $access_token);
					return $access_token;
				}
			}

			// signed request states there's no access token, so anything
			// stored should be cleared.
			$this -> clearAllPersistentData();
			return false;
			// respect the signed request's data, even
			// if there's an authorization code or something else
		}

		$code = $this -> getCode();
		if ($code && $code != $this -> getPersistentData('code'))
		{
			$access_token = $this -> getAccessTokenFromCode($code);
			if ($access_token)
			{
				$this -> setPersistentData('code', $code);
				$this -> setPersistentData('access_token', $access_token);
				return $access_token;
			}

			// code was bogus, so everything based on it should be invalidated.
			$this -> clearAllPersistentData();
			return false;
		}

		// as a fallback, just return whatever is in the persistent
		// store, knowing nothing explicit (signed request, authorization
		// code, etc.) was present to shadow it (or we saw a code in $_REQUEST,
		// but it's the same as what's in the persistent store)
		return $this -> getPersistentData('access_token');
	}

	/**
	 * Retrieve the signed request, either from a request parameter or,
	 * if not present, from a cookie.
	 *
	 * @return string the signed request, if available, or null otherwise.
	 */
	public function getSignedRequest()
	{
		if (!$this -> signedRequest)
		{
			if (isset($_REQUEST['signed_request']))
			{
				$this -> signedRequest = $this -> parseSignedRequest($_REQUEST['signed_request']);
			}
			else
			if (isset($_COOKIE[$this -> getSignedRequestCookieName()]))
			{
				$this -> signedRequest = $this -> parseSignedRequest($_COOKIE[$this -> getSignedRequestCookieName()]);
			}
		}
		return $this -> signedRequest;
	}

	/**
	 * Get the UID of the connected user, or 0
	 * if the Facebook user is not connected.
	 *
	 * @return string the UID if available.
	 */
	public function getUser()
	{
		if ($this -> user !== null)
		{
			// we've already determined this and cached the value.
			return $this -> user;
		}

		return $this -> user = $this -> getUserFromAvailableData();
	}

	/**
	 * Determines the connected user by first examining any signed
	 * requests, then considering an authorization code, and then
	 * falling back to any persistent store storing the user.
	 *
	 * @return integer The id of the connected Facebook user,
	 *                 or 0 if no such user exists.
	 */
	protected function getUserFromAvailableData()
	{
		// if a signed request is supplied, then it solely determines
		// who the user is.
		$signed_request = $this -> getSignedRequest();
		if ($signed_request)
		{
			if (array_key_exists('user_id', $signed_request))
			{
				$user = $signed_request['user_id'];
				$this -> setPersistentData('user_id', $signed_request['user_id']);
				return $user;
			}

			// if the signed request didn't present a user id, then invalidate
			// all entries in any persistent store.
			$this -> clearAllPersistentData();
			return 0;
		}

		$user = $this -> getPersistentData('user_id', $default = 0);
		$persisted_access_token = $this -> getPersistentData('access_token');

		// use access_token to fetch user id if we have a user access_token, or if
		// the cached access token has changed.
		$access_token = $this -> getAccessToken();
		if ($access_token && $access_token != $this -> getApplicationAccessToken() && !($user && $persisted_access_token == $access_token))
		{
			$user = $this -> getUserFromAccessToken();
			if ($user)
			{
				$this -> setPersistentData('user_id', $user);
			}
			else
			{
				$this -> clearAllPersistentData();
			}
		}

		return $user;
	}

	/**
	 * Get a Login URL for use with redirects. By default, full page redirect is
	 * assumed. If you are using the generated URL with a window.open() call in
	 * JavaScript, you can pass in display=popup as part of the $params.
	 *
	 * The parameters:
	 * - redirect_uri: the url to go to after a successful login
	 * - scope: comma separated list of requested extended perms
	 *
	 * @param array $params Provide custom parameters
	 * @return string The URL for the login flow
	 */
	public function getLoginUrl($params = array())
	{
		$this -> establishCSRFTokenState();
		$currentUrl = $this -> getCurrentUrl();

		// if 'scope' is passed as an array, convert to comma separated list
		$scopeParams = isset($params['scope']) ? $params['scope'] : null;
		if ($scopeParams && is_array($scopeParams))
		{
			$params['scope'] = implode(',', $scopeParams);
		}

		return $this -> getUrl('www', 'dialog/oauth', array_merge(array(
			'client_id' => $this -> getAppId(),
			'redirect_uri' => $currentUrl, // possibly overwritten
			'state' => $this -> state
		), $params));
	}

	/**
	 * Get a Logout URL suitable for use with redirects.
	 *
	 * The parameters:
	 * - next: the url to go to after a successful logout
	 *
	 * @param array $params Provide custom parameters
	 * @return string The URL for the logout flow
	 */
	public function getLogoutUrl($params = array())
	{
		return $this -> getUrl('www', 'logout.php', array_merge(array(
			'next' => $this -> getCurrentUrl(),
			'access_token' => $this -> getUserAccessToken(),
		), $params));
	}

	/**
	 * Get a login status URL to fetch the status from Facebook.
	 *
	 * The parameters:
	 * - ok_session: the URL to go to if a session is found
	 * - no_session: the URL to go to if the user is not connected
	 * - no_user: the URL to go to if the user is not signed into facebook
	 *
	 * @param array $params Provide custom parameters
	 * @return string The URL for the logout flow
	 */
	public function getLoginStatusUrl($params = array())
	{
		return $this -> getUrl('www', 'extern/login_status.php', array_merge(array(
			'api_key' => $this -> getAppId(),
			'no_session' => $this -> getCurrentUrl(),
			'no_user' => $this -> getCurrentUrl(),
			'ok_session' => $this -> getCurrentUrl(),
			'session_version' => 3,
		), $params));
	}

	/**
	 * Make an API call.
	 *
	 * @return mixed The decoded response
	 */
	public function api(/* polymorphic */)
	{
		$args = func_get_args();
		if (is_array($args[0]))
		{
			return $this -> _restserver($args[0]);
		}
		else
		{
			return call_user_func_array(array(
				$this,
				'_graph'
			), $args);
		}
	}

	/**
	 * Constructs and returns the name of the cookie that
	 * potentially houses the signed request for the app user.
	 * The cookie is not set by the BaseFacebook class, but
	 * it may be set by the JavaScript SDK.
	 *
	 * @return string the name of the cookie that would house
	 *         the signed request value.
	 */
	protected function getSignedRequestCookieName()
	{
		return 'fbsr_' . $this -> getAppId();
	}

	/**
	 * Constructs and returns the name of the coookie that potentially contain
	 * metadata. The cookie is not set by the BaseFacebook class, but it may be
	 * set by the JavaScript SDK.
	 *
	 * @return string the name of the cookie that would house metadata.
	 */
	protected function getMetadataCookieName()
	{
		return 'fbm_' . $this -> getAppId();
	}

	/**
	 * Get the authorization code from the query parameters, if it exists,
	 * and otherwise return false to signal no authorization code was
	 * discoverable.
	 *
	 * @return mixed The authorization code, or false if the authorization
	 *               code could not be determined.
	 */
	protected function getCode()
	{
		if (isset($_REQUEST['code']))
		{
			if ($this -> state !== null && isset($_REQUEST['state']) && $this -> state === $_REQUEST['state'])
			{

				// CSRF state has done its job, so clear it
				$this -> state = null;
				$this -> clearPersistentData('state');
				return $_REQUEST['code'];
			}
			else
			{
				self::errorLog('CSRF state token does not match one provided.');
				return false;
			}
		}

		return false;
	}

	/**
	 * Retrieves the UID with the understanding that
	 * $this->accessToken has already been set and is
	 * seemingly legitimate.  It relies on Facebook's Graph API
	 * to retrieve user information and then extract
	 * the user ID.
	 *
	 * @return integer Returns the UID of the Facebook user, or 0
	 *                 if the Facebook user could not be determined.
	 */
	protected function getUserFromAccessToken()
	{
		try
		{
			$user_info = $this -> api('/me');
			return $user_info['id'];
		}
		catch (FacebookApiException $e)
		{
			return 0;
		}
	}

	/**
	 * Returns the access token that should be used for logged out
	 * users when no authorization code is available.
	 *
	 * @return string The application access token, useful for gathering
	 *                public information about users and applications.
	 */
	protected function getApplicationAccessToken()
	{
		return $this -> appId . '|' . $this -> appSecret;
	}

	/**
	 * Lays down a CSRF state token for this process.
	 *
	 * @return void
	 */
	protected function establishCSRFTokenState()
	{
		if ($this -> state === null)
		{
			$this -> state = md5(uniqid(mt_rand(), true));
			$this -> setPersistentData('state', $this -> state);
		}
	}

	/**
	 * Retrieves an access token for the given authorization code
	 * (previously generated from www.facebook.com on behalf of
	 * a specific user).  The authorization code is sent to graph.facebook.com
	 * and a legitimate access token is generated provided the access token
	 * and the user for which it was generated all match, and the user is
	 * either logged in to Facebook or has granted an offline access permission.
	 *
	 * @param string $code An authorization code.
	 * @return mixed An access token exchanged for the authorization code, or
	 *               false if an access token could not be generated.
	 */
	protected function getAccessTokenFromCode($code, $redirect_uri = null)
	{
		if (empty($code))
		{
			return false;
		}

		if ($redirect_uri === null)
		{
			$redirect_uri = $this -> getCurrentUrl();
		}

		try
		{
			// need to circumvent json_decode by calling _oauthRequest
			// directly, since response isn't JSON format.
			$access_token_response = $this -> _oauthRequest($this -> getUrl('graph', '/oauth/access_token'), $params = array(
				'client_id' => $this -> getAppId(),
				'client_secret' => $this -> getAppSecret(),
				'redirect_uri' => $redirect_uri,
				'code' => $code
			));
		}
		catch (FacebookApiException $e)
		{
			// most likely that user very recently revoked authorization.
			// In any event, we don't have an access token, so say so.
			return false;
		}

		if (empty($access_token_response))
		{
			return false;
		}

		$response_params = array();
		parse_str($access_token_response, $response_params);
		if (!isset($response_params['access_token']))
		{
			return false;
		}

		return $response_params['access_token'];
	}

	/**
	 * Invoke the old restserver.php endpoint.
	 *
	 * @param array $params Method call object
	 *
	 * @return mixed The decoded response object
	 * @throws FacebookApiException
	 */
	protected function _restserver($params)
	{
		// generic application level parameters
		$params['api_key'] = $this -> getAppId();
		$params['format'] = 'json-strings';

		$result = json_decode($this -> _oauthRequest($this -> getApiUrl($params['method']), $params), true);

		// results are returned, errors are thrown
		if (is_array($result) && isset($result['error_code']))
		{
			$this -> throwAPIException($result);
			// @codeCoverageIgnoreStart
		}
		// @codeCoverageIgnoreEnd

		$method = strtolower($params['method']);
		if ($method === 'auth.expiresession' || $method === 'auth.revokeauthorization')
		{
			$this -> destroySession();
		}

		return $result;
	}

	/**
	 * Return true if this is video post.
	 *
	 * @param string $path The path
	 * @param string $method The http method (default 'GET')
	 *
	 * @return boolean true if this is video post
	 */
	protected function isVideoPost($path, $method = 'GET')
	{
		if ($method == 'POST' && preg_match("/^(\/)(.+)(\/)(videos)$/", $path))
		{
			return true;
		}
		return false;
	}

	/**
	 * Invoke the Graph API.
	 *
	 * @param string $path The path (required)
	 * @param string $method The http method (default 'GET')
	 * @param array $params The query/post data
	 *
	 * @return mixed The decoded response object
	 * @throws FacebookApiException
	 */
	protected function _graph($path, $method = 'GET', $params = array())
	{
		if (is_array($method) && empty($params))
		{
			$params = $method;
			$method = 'GET';
		}
		$params['method'] = $method;
		// method override as we always do a POST

		if ($this -> isVideoPost($path, $method))
		{
			$domainKey = 'graph_video';
		}
		else
		{
			$domainKey = 'graph';
		}

		$result = json_decode($this -> _oauthRequest($this -> getUrl($domainKey, $path), $params), true);

		// results are returned, errors are thrown
		if (is_array($result) && isset($result['error']))
		{
			$this -> throwAPIException($result);
			// @codeCoverageIgnoreStart
		}
		// @codeCoverageIgnoreEnd

		return $result;
	}

	/**
	 * Make a OAuth Request.
	 *
	 * @param string $url The path (required)
	 * @param array $params The query/post data
	 *
	 * @return string The decoded response object
	 * @throws FacebookApiException
	 */
	protected function _oauthRequest($url, $params)
	{
		if (!isset($params['access_token']))
		{
			$params['access_token'] = $this -> getAccessToken();
		}

		// json_encode all params values that are not strings
		foreach ($params as $key => $value)
		{
			if (!is_string($value))
			{
				$params[$key] = json_encode($value);
			}
		}

		return $this -> makeRequest($url, $params);
	}

	/**
	 * Makes an HTTP request. This method can be overridden by subclasses if
	 * developers want to do fancier things or use something other than curl to
	 * make the request.
	 *
	 * @param string $url The URL to make the request to
	 * @param array $params The parameters to use for the POST body
	 * @param CurlHandler $ch Initialized curl handle
	 *
	 * @return string The response text
	 */
	protected function makeRequest($url, $params, $ch = null)
	{
		if (!$ch)
		{
			$ch = curl_init();
		}

		$opts = self::$CURL_OPTS;
		if ($this -> getFileUploadSupport())
		{
			$opts[CURLOPT_POSTFIELDS] = $params;
		}
		else
		{
			$opts[CURLOPT_POSTFIELDS] = http_build_query($params, null, '&');
		}
		$opts[CURLOPT_URL] = $url;

		// disable the 'Expect: 100-continue' behaviour. This causes CURL to wait
		// for 2 seconds if the server does not support this header.
		if (isset($opts[CURLOPT_HTTPHEADER]))
		{
			$existing_headers = $opts[CURLOPT_HTTPHEADER];
			$existing_headers[] = 'Expect:';
			$opts[CURLOPT_HTTPHEADER] = $existing_headers;
		}
		else
		{
			$opts[CURLOPT_HTTPHEADER] = array('Expect:');
		}

		curl_setopt_array($ch, $opts);
		$result = curl_exec($ch);

		if (curl_errno($ch) == 60)
		{
			// CURLE_SSL_CACERT
			self::errorLog('Invalid or no certificate authority found, ' . 'using bundled information');
			curl_setopt($ch, CURLOPT_CAINFO, dirname(__FILE__) . '/fb_ca_chain_bundle.crt');
			$result = curl_exec($ch);
		}

		// With dual stacked DNS responses, it's possible for a server to
		// have IPv6 enabled but not have IPv6 connectivity.  If this is
		// the case, curl will try IPv4 first and if that fails, then it will
		// fall back to IPv6 and the error EHOSTUNREACH is returned by the
		// operating system.
		if ($result === false && empty($opts[CURLOPT_IPRESOLVE]))
		{
			$matches = array();
			$regex = '/Failed to connect to ([^:].*): Network is unreachable/';
			if (preg_match($regex, curl_error($ch), $matches))
			{
				if (strlen(@inet_pton($matches[1])) === 16)
				{
					self::errorLog('Invalid IPv6 configuration on server, ' . 'Please disable or get native IPv6 on your server.');
					self::$CURL_OPTS[CURLOPT_IPRESOLVE] = CURL_IPRESOLVE_V4;
					curl_setopt($ch, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);
					$result = curl_exec($ch);
				}
			}
		}

		if ($result === false)
		{
			$e = new FacebookApiException( array(
				'error_code' => curl_errno($ch),
				'error' => array(
					'message' => curl_error($ch),
					'type' => 'CurlException',
				),
			));
			curl_close($ch);
			throw $e;
		}
		curl_close($ch);
		return $result;
	}

	/**
	 * Parses a signed_request and validates the signature.
	 *
	 * @param string $signed_request A signed token
	 * @return array The payload inside it or null if the sig is wrong
	 */
	protected function parseSignedRequest($signed_request)
	{
		list($encoded_sig, $payload) = explode('.', $signed_request, 2);

		// decode the data
		$sig = self::base64UrlDecode($encoded_sig);
		$data = json_decode(self::base64UrlDecode($payload), true);

		if (strtoupper($data['algorithm']) !== self::SIGNED_REQUEST_ALGORITHM)
		{
			self::errorLog('Unknown algorithm. Expected ' . self::SIGNED_REQUEST_ALGORITHM);
			return null;
		}

		// check sig
		$expected_sig = hash_hmac('sha256', $payload, $this -> getAppSecret(), $raw = true);
		if ($sig !== $expected_sig)
		{
			self::errorLog('Bad Signed JSON signature!');
			return null;
		}

		return $data;
	}

	/**
	 * Makes a signed_request blob using the given data.
	 *
	 * @param array The data array.
	 * @return string The signed request.
	 */
	protected function makeSignedRequest($data)
	{
		if (!is_array($data))
		{
			throw new InvalidArgumentException('makeSignedRequest expects an array. Got: ' . print_r($data, true));
		}
		$data['algorithm'] = self::SIGNED_REQUEST_ALGORITHM;
		$data['issued_at'] = time();
		$json = json_encode($data);
		$b64 = self::base64UrlEncode($json);
		$raw_sig = hash_hmac('sha256', $b64, $this -> getAppSecret(), $raw = true);
		$sig = self::base64UrlEncode($raw_sig);
		return $sig . '.' . $b64;
	}

	/**
	 * Build the URL for api given parameters.
	 *
	 * @param $method String the method name.
	 * @return string The URL for the given parameters
	 */
	protected function getApiUrl($method)
	{
		static $READ_ONLY_CALLS = array(
			'admin.getallocation' => 1,
			'admin.getappproperties' => 1,
			'admin.getbannedusers' => 1,
			'admin.getlivestreamvialink' => 1,
			'admin.getmetrics' => 1,
			'admin.getrestrictioninfo' => 1,
			'application.getpublicinfo' => 1,
			'auth.getapppublickey' => 1,
			'auth.getsession' => 1,
			'auth.getsignedpublicsessiondata' => 1,
			'comments.get' => 1,
			'connect.getunconnectedfriendscount' => 1,
			'dashboard.getactivity' => 1,
			'dashboard.getcount' => 1,
			'dashboard.getglobalnews' => 1,
			'dashboard.getnews' => 1,
			'dashboard.multigetcount' => 1,
			'dashboard.multigetnews' => 1,
			'data.getcookies' => 1,
			'events.get' => 1,
			'events.getmembers' => 1,
			'fbml.getcustomtags' => 1,
			'feed.getappfriendstories' => 1,
			'feed.getregisteredtemplatebundlebyid' => 1,
			'feed.getregisteredtemplatebundles' => 1,
			'fql.multiquery' => 1,
			'fql.query' => 1,
			'friends.arefriends' => 1,
			'friends.get' => 1,
			'friends.getappusers' => 1,
			'friends.getlists' => 1,
			'friends.getmutualfriends' => 1,
			'gifts.get' => 1,
			'groups.get' => 1,
			'groups.getmembers' => 1,
			'intl.gettranslations' => 1,
			'links.get' => 1,
			'notes.get' => 1,
			'notifications.get' => 1,
			'pages.getinfo' => 1,
			'pages.isadmin' => 1,
			'pages.isappadded' => 1,
			'pages.isfan' => 1,
			'permissions.checkavailableapiaccess' => 1,
			'permissions.checkgrantedapiaccess' => 1,
			'photos.get' => 1,
			'photos.getalbums' => 1,
			'photos.gettags' => 1,
			'profile.getinfo' => 1,
			'profile.getinfooptions' => 1,
			'stream.get' => 1,
			'stream.getcomments' => 1,
			'stream.getfilters' => 1,
			'users.getinfo' => 1,
			'users.getloggedinuser' => 1,
			'users.getstandardinfo' => 1,
			'users.hasapppermission' => 1,
			'users.isappuser' => 1,
			'users.isverified' => 1,
			'video.getuploadlimits' => 1
		);
		$name = 'api';
		if (isset($READ_ONLY_CALLS[strtolower($method)]))
		{
			$name = 'api_read';
		}
		else
		if (strtolower($method) == 'video.upload')
		{
			$name = 'api_video';
		}
		return self::getUrl($name, 'restserver.php');
	}

	/**
	 * Build the URL for given domain alias, path and parameters.
	 *
	 * @param $name string The name of the domain
	 * @param $path string Optional path (without a leading slash)
	 * @param $params array Optional query parameters
	 *
	 * @return string The URL for the given parameters
	 */
	protected function getUrl($name, $path = '', $params = array())
	{
		$url = self::$DOMAIN_MAP[$name];
		if ($path)
		{
			if ($path[0] === '/')
			{
				$path = substr($path, 1);
			}
			$url .= $path;
		}
		if ($params)
		{
			$url .= '?' . http_build_query($params, null, '&');
		}

		return $url;
	}

	protected function getHttpHost()
	{
		if ($this -> trustForwarded && isset($_SERVER['HTTP_X_FORWARDED_HOST']))
		{
			return $_SERVER['HTTP_X_FORWARDED_HOST'];
		}
		return $_SERVER['HTTP_HOST'];
	}

	protected function getHttpProtocol()
	{
		if ($this -> trustForwarded && isset($_SERVER['HTTP_X_FORWARDED_PROTO']))
		{
			if ($_SERVER['HTTP_X_FORWARDED_PROTO'] === 'https')
			{
				return 'https';
			}
			return 'http';
		}
		if (isset($_SERVER['HTTPS']) && ($_SERVER['HTTPS'] === 'on' || $_SERVER['HTTPS'] == 1))
		{
			return 'https';
		}
		return 'http';
	}

	/**
	 * Get the base domain used for the cookie.
	 */
	protected function getBaseDomain()
	{
		// The base domain is stored in the metadata cookie if not we fallback
		// to the current hostname
		$metadata = $this -> getMetadataCookie();
		if (array_key_exists('base_domain', $metadata) && !empty($metadata['base_domain']))
		{
			return trim($metadata['base_domain'], '.');
		}
		return $this -> getHttpHost();
	}

	/**

	 /**
	 * Returns the Current URL, stripping it of known FB parameters that should
	 * not persist.
	 *
	 * @return string The current URL
	 */
	protected function getCurrentUrl()
	{
		$protocol = $this -> getHttpProtocol() . '://';
		$host = $this -> getHttpHost();
		$currentUrl = $protocol . $host . $_SERVER['REQUEST_URI'];
		$parts = parse_url($currentUrl);

		$query = '';
		if (!empty($parts['query']))
		{
			// drop known fb params
			$params = explode('&', $parts['query']);
			$retained_params = array();
			foreach ($params as $param)
			{
				if ($this -> shouldRetainParam($param))
				{
					$retained_params[] = $param;
				}
			}

			if (!empty($retained_params))
			{
				$query = '?' . implode($retained_params, '&');
			}
		}

		// use port if non default
		$port = isset($parts['port']) && (($protocol === 'http://' && $parts['port'] !== 80) || ($protocol === 'https://' && $parts['port'] !== 443)) ? ':' . $parts['port'] : '';

		// rebuild
		return $protocol . $parts['host'] . $port . $parts['path'] . $query;
	}

	/**
	 * Returns true if and only if the key or key/value pair should
	 * be retained as part of the query string.  This amounts to
	 * a brute-force search of the very small list of Facebook-specific
	 * params that should be stripped out.
	 *
	 * @param string $param A key or key/value pair within a URL's query (e.g.
	 *                     'foo=a', 'foo=', or 'foo'.
	 *
	 * @return boolean
	 */
	protected function shouldRetainParam($param)
	{
		foreach (self::$DROP_QUERY_PARAMS as $drop_query_param)
		{
			if (strpos($param, $drop_query_param . '=') === 0)
			{
				return false;
			}
		}

		return true;
	}

	/**
	 * Analyzes the supplied result to see if it was thrown
	 * because the access token is no longer valid.  If that is
	 * the case, then we destroy the session.
	 *
	 * @param $result array A record storing the error message returned
	 *                      by a failed API call.
	 */
	protected function throwAPIException($result)
	{
		$e = new FacebookApiException($result);
		switch ($e->getType())
		{
			// OAuth 2.0 Draft 00 style
			case 'OAuthException' :
			// OAuth 2.0 Draft 10 style
			case 'invalid_token' :
			// REST server errors are just Exceptions
			case 'Exception' :
				$message = $e -> getMessage();
				if ((strpos($message, 'Error validating access token') !== false) || (strpos($message, 'Invalid OAuth access token') !== false) || (strpos($message, 'An active access token must be used') !== false))
				{
					$this -> destroySession();
				}
				break;
		}

		throw $e;
	}

	/**
	 * Prints to the error log if you aren't in command line mode.
	 *
	 * @param string $msg Log message
	 */
	protected static function errorLog($msg)
	{
		// disable error log if we are running in a CLI environment
		// @codeCoverageIgnoreStart
		if (php_sapi_name() != 'cli')
		{
			error_log($msg);
		}
		// uncomment this if you want to see the errors on the page
		// print 'error_log: '.$msg."\n";
		// @codeCoverageIgnoreEnd
	}

	/**
	 * Base64 encoding that doesn't need to be urlencode()ed.
	 * Exactly the same as base64_encode except it uses
	 *   - instead of +
	 *   _ instead of /
	 *   No padded =
	 *
	 * @param string $input base64UrlEncoded string
	 * @return string
	 */
	protected static function base64UrlDecode($input)
	{
		return base64_decode(strtr($input, '-_', '+/'));
	}

	/**
	 * Base64 encoding that doesn't need to be urlencode()ed.
	 * Exactly the same as base64_encode except it uses
	 *   - instead of +
	 *   _ instead of /
	 *
	 * @param string $input string
	 * @return string base64Url encoded string
	 */
	protected static function base64UrlEncode($input)
	{
		$str = strtr(base64_encode($input), '+/', '-_');
		$str = str_replace('=', '', $str);
		return $str;
	}

	/**
	 * Destroy the current session
	 */
	public function destroySession()
	{
		$this -> accessToken = null;
		$this -> signedRequest = null;
		$this -> user = null;
		$this -> clearAllPersistentData();

		// Javascript sets a cookie that will be used in getSignedRequest that we
		// need to clear if we can
		$cookie_name = $this -> getSignedRequestCookieName();
		if (array_key_exists($cookie_name, $_COOKIE))
		{
			unset($_COOKIE[$cookie_name]);
			if (!headers_sent())
			{
				$base_domain = $this -> getBaseDomain();
				setcookie($cookie_name, '', 1, '/', '.' . $base_domain);
			}
			else
			{
				// @codeCoverageIgnoreStart
				self::errorLog('There exists a cookie that we wanted to clear that we couldn\'t ' . 'clear because headers was already sent. Make sure to do the first ' . 'API call before outputing anything.');
				// @codeCoverageIgnoreEnd
			}
		}
	}

	/**
	 * Parses the metadata cookie that our Javascript API set
	 *
	 * @return  an array mapping key to value
	 */
	protected function getMetadataCookie()
	{
		$cookie_name = $this -> getMetadataCookieName();
		if (!array_key_exists($cookie_name, $_COOKIE))
		{
			return array();
		}

		// The cookie value can be wrapped in "-characters so remove them
		$cookie_value = trim($_COOKIE[$cookie_name], '"');

		if (empty($cookie_value))
		{
			return array();
		}

		$parts = explode('&', $cookie_value);
		$metadata = array();
		foreach ($parts as $part)
		{
			$pair = explode('=', $part, 2);
			if (!empty($pair[0]))
			{
				$metadata[urldecode($pair[0])] = (count($pair) > 1) ? urldecode($pair[1]) : '';
			}
		}

		return $metadata;
	}

	protected static function isAllowedDomain($big, $small)
	{
		if ($big === $small)
		{
			return true;
		}
		return self::endsWith($big, '.' . $small);
	}

	protected static function endsWith($big, $small)
	{
		$len = strlen($small);
		if ($len === 0)
		{
			return true;
		}
		return substr($big, -$len) === $small;
	}

	/**
	 * Each of the following four methods should be overridden in
	 * a concrete subclass, as they are in the provided Facebook class.
	 * The Facebook class uses PHP sessions to provide a primitive
	 * persistent store, but another subclass--one that you implement--
	 * might use a database, memcache, or an in-memory cache.
	 *
	 * @see Facebook
	 */

	/**
	 * Stores the given ($key, $value) pair, so that future calls to
	 * getPersistentData($key) return $value. This call may be in another request.
	 *
	 * @param string $key
	 * @param array $value
	 *
	 * @return void
	 */
	abstract protected function setPersistentData($key, $value);

	/**
	 * Get the data for $key, persisted by BaseFacebook::setPersistentData()
	 *
	 * @param string $key The key of the data to retrieve
	 * @param boolean $default The default value to return if $key is not found
	 *
	 * @return mixed
	 */
	abstract protected function getPersistentData($key, $default = false);

	/**
	 * Clear the data with $key from the persistent storage
	 *
	 * @param string $key
	 * @return void
	 */
	abstract protected function clearPersistentData($key);

	/**
	 * Clear all data from the persistent storage
	 *
	 * @return void
	 */
	abstract protected function clearAllPersistentData();
}
